Fuel cells have been proposed as a clean, efficient and environmentally responsible power source for electric vehicles and various other applications. In particular, fuel cells have been identified as a potential alternative for the traditional internal-combustion engine used in automobiles.
A fuel cell typically includes three basic components: a cathode, an anode, and an electrolyte membrane. The electrolyte membrane is sandwiched between the cathode and the anode to form a membrane-electrolyte-assembly (MEA). Hydrogen at the anode is converted to positively-charged hydrogen ions. These ions travel through the electrolyte to the cathode, where they react with oxygen. The oxygen can be supplied from air, for example. The remaining electrons in the anode flow through an external circuit to the cathode, where they join the oxygen and the hydrogen protons to form water. Individual fuel cells can be stacked together in series to form a fuel cell stack capable of supplying sufficient amounts of electricity.
Fuel cell stacks are characterized by a specific operating temperature which presents a significant design challenge, particularly with respect to a structural and an operational integrity of the fuel cell stack. Maintaining the fuel cell stack within the temperature ranges that are necessary for optimum fuel cell operation generally requires employment of a cooling system.
The cooling systems known for both internal combustion engines and fuel cell systems typically utilize a radiator having a plurality of channels through which a coolant from a combustion engine or fuel cell stack may flow for cooling. The radiator generally includes an electrically driven fan which is mounted adjacent the radiator channels and employed to reduce a temperature of the coolant as the coolant passes through the radiator. The electrical fans can be variable speed and increase in power proportionally as the temperature of the coolant from the fuel cell stack increases. However, it is known that the electrical fans can emit noise at an unacceptable level, particularly when the electrical fans are high-power or have large rotor diameters. The noise can be undesirable for both passengers in a vehicle employing the cooling system and for pedestrians in proximity of the vehicle.
A fuel cell system having a fan shroud and barrel combination with built-in silencers, e.g. Helmholtz resonators, is reported by Shah et al. in U.S. Pat. No. 6,896,095. The fan shroud can be used to reduce a noise associated with an air-moving device such as an axial flow fan employed in a cooling system.
U.S. Pat. No. 6,651,761 to Hrovat et al. describes a system and method for controlling a coolant temperature of two independent cooling loops of a fuel cell vehicle by adjusting at the system pump speed, fan speed, and radiator bypass valve position. Multiple feedback controllers coordinated by flip-flop logic are used to minimize energy consumption and provide optimal control system performance with respect to fan speed and valve position plant inputs.
There is a continuing need for a fuel cell system and method that provides a desired cooling performance with a minimized noise emission. Desirably, the fuel cell system militates against damaging of the fuel cell system caused by an undesirable operating temperature.